In recent years, several broadband wireless technologies have been developed to meet growing number of broadband subscribers and to provide more and better applications and services. For example, the 3rd Generation Partnership Project 2 (3GPP2) developed Code Division Multiple Access 2000 (CDMA 2000), 1× Evolution Data Optimized (1× EVDO) and Ultra Mobile Broadband (UMB) systems. The 3GPP developed Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), and Long Term Evolution (LTE) systems. The Institute of Electrical and Electronics Engineers (IEEE) developed Mobile Worldwide Interoperability for Microwave Access (WiMAX) systems. As more and more people become users of mobile communication systems and more and more services are provided over these systems, there is an increasing need for a mobile communication system with large capacity, high throughput, lower latency, and better reliability.
A Super Mobile Broadband (SMB) system based on millimeter waves, i.e., radio waves with wavelength in range of 1 millimeter (mm) to 10 mm, which corresponds to a radio frequency of 30 Gigahertz (GHz) to 300 GHz, is a candidate for next generation mobile communication technology as vast amount of spectrum is available in a millimeter Wave band. In general, an SMB network consists of multiple SMB Base Stations (BSs) that cover a geographic area. In order to ensure good coverage, SMB base stations need to be deployed with a higher density than macro-cellular base stations. In general, SMB base stations are recommended to be deployed roughly the same site-to-site distance as microcell or Pico-cell deployment in an urban environment. Typically, transmission and/or reception in an SMB system are based on narrow beams, which suppress the interference from neighboring SMB base stations and extend the range of an SMB link. However due to a high path loss, a heavy shadowing, and rain attenuation, reliable transmission at higher frequencies is one of the key issues that need to be overcome in order to make SMB system a practical reality.
Lower frequencies in a cellular band having robust link characteristics can be utilized with higher frequencies in an mmWave band to overcome reliability issues in the SMB system. In an asymmetric multicarrier communication network environment, a Mobile Station (MS) communicates with a BS using asymmetric multiband carriers consisting of at least one low frequency carrier in the cellular band and at least one high frequency carrier in the mmWave band. A primary carrier i.e., a carrier operating on low frequencies and a secondary carrier i.e., carrier operating on high frequencies may be transmitted by the same BS or a different BS. Since the transmission characteristics of low frequency carriers in the cellular band and high frequency carriers in the mmWave band are quite different, Transmission Time Intervals (TTIs) and frame structures for the primary carrier and the secondary carrier may not be same.
In an asymmetric multicarrier SMB network, a low frequency carrier in a cellular band can be used to signal resource allocation information for a high frequency carrier in an mmWave band for reliable signaling of the resource allocation information. Since, the bandwidth, frame structure, TTI and resource block design of the low frequency carrier is different from that of high frequency carrier, control information indicating the resource allocation for an MS is different for the low frequency carrier and the high frequency carrier.
For a low frequency carrier (e.g., an LTE carrier), fields for signaling resource allocation information are defined using Downlink Control Information (DCI) formats. Several DCI formats are currently used for signaling unicast resource allocation information for the low frequency carrier to the MS. Each of these DCI formats are distinguished from each other based on the size of each DCI format.
In a multicarrier network of the related art, unicast DCI encoded in one of the DCI formats is transmitted in a Physical Downlink Control Channel (PDCCH) of a primary carrier, wherein the DCI corresponds to unicast resource allocation information associated with an MS. Each PDCCH carries a single DCI encoded in one of the DCI formats for the primary carrier or the secondary carrier of the multicarrier network of the related art. The carrier for which the unicast DCI transmitted in the PDCCH is intended is indicated to the MS in a carrier index field of the DCI format encoding the unicast DCI. Each carrier assigned to the mobile station is identified by a distinct carrier index via the carrier index field in the DCI format. The PDCCH carrying the unicast DCI for the MS is a Cyclic Redundancy Check (CRC) masked with a unicast Cellular Radio Network Temporary Identifier (C-RNTI) assigned to the MS. Further, multiple PDCCHs may be transmitted in one scheduling interval of the primary carrier.
Typically, in the multicarrier network of the related art, unicast DCI intended for both the primary carrier and the secondary carrier is encoded in the same DCI format. This is possible as both the primary carrier and the secondary carrier are symmetric in nature from perspective of a resource block design, TTI, and frame structure. However, in an asymmetric multicarrier communication network, the DCI format defined for primary carrier cannot be used for secondary carrier as a resource block design, TTI, and frame structure is not the same for the primary carrier and the secondary carrier.
Therefore, a need exists for a method and an apparatus for communicating downlink control information in an asymmetric multicarrier communication network environment.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.